The present invention relates to aircraft engine systems and, more particularly, to an electric starter/generator for aircraft, tank engines, and other mobile vehicles.
Brushless dc machines require electronic commutation in order to operate properly. Existing bridge-type or bifilar type inverter/converter units are used to electronically commutate a switched reluctance machine to produce direct current electrical power at only one voltage level at a time when in the generating mode. This creates a problem for vehicles that require dc power of at least two different voltage levels, most commonly 270 vdc and 28 vdc.
Present day switched reluctance machines typically generate electric power at one voltage level. With bifilar type inverter/converter units, close magnetic coupling between the bifilar windings is required so that the power switches will not be subjected to high and potentially damaging voltages resulting from electronic switching. Unfortunately, present technology of machines with bifilar windings use separate windings with a certain amount of average physical separation between the windings which results in looseness in the magnetic coupling of the bifilar windings. This looseness in magnetic coupling between the bifilar windings in the machine results in leakage inductances that can cause undesirable effects such as overvoltages on components, particularly power transistors during switching events. Also, higher leakage inductances cause increased power losses and reduced efficiencies.
Existing machines have further limitations as well. For example, an electric power system, particularly in a vehicle, may require electric power at two or more voltage levels. One means for providing the two different voltage levels is to use an additional, external converter to convert electrical power from one voltage level to another. Unfortunately, the application of an external converter is an inefficient use of components, since it adds cost and volume to the system and reduces reliability.
It is therefore highly desirable and an object of the present invention to provide multiple voltage levels without the addition of an external converter.
Another object of the present invention is to provide simultaneous multiple voltage levels for electronically commutated electrical machines.
Another object of the present invention is to improve magnetic coupling between bifilar windings inside electromechanical machines.
Another object of the present invention is to optimize electric power systems to engine and aircraft applications, extending design flexibility.
These objects and other features and advantages will become more readily apparent in the following description when taken in conjunction with the appended drawings.